It is well recognized that various conditions within various substances have or produce electrical effects which, if monitorable, can give an indication of the nature of such an internal condition. For example, it is known that conditions within various parts of the human body have electrical characteristics, such as differing impedances, which directly reflect such conditions. Further, conditions such as cracks and/or other flaws in various materials have or produce directly related electrical characteristics.
It is desirable to be able, in many instances, to follow, detect or monitor such conditions in a nonevasive, noncontacting, nondamaging manner.
While it is recognized that there are many applications for the apparatus and method of the invention, a preferred embodiment and method are described herein in connection with monitoringconditions within a portion of a human body, such as within a person's heart. This is a field in which the invention has been found to have particular utility.
The present invention recognizes and takes advantage of a well-known standing-wave phenomenon present with electromagnetic radiation wherein, at predetermined regular wavelength-related intervals along a transmission medium, wherein such radiation is present, directly related electrical voltage and current conditions exist. This phenomenon, and the theory underlying the instant invention, are set forth in many texts, including Electronic and Radio Engineering (4th Ed. 1955), Secs. 4-11 (McGraw-Hill Electrical and Electronic Engineering Series); and W. Johnson, Transmission Lines and Networks (1950), (McGraw-Hill Electrical and Electronic Engineering Series). There is proposed for use in the present invention a bidirectional microwave antenna which is capable of bidirectionally radiating and focusing microwave energy at a pair of spaced focal points that are spaced apart by a distance substantially equaling one-half the wavelength of the radiated energy. The antenna features a central ring-like radiation-effective expanse which functions as the driven element in the antenna, and in conjunction with this expanse director rings and a focusing lens that produce simultaneously on opposite sides of the antenna the two focal points just mentioned.
Working in conjunction with this antenna is a tubular receiver which is located adjacent one of the focal points, and which has a size that defines, in essence, the overall resolution of the system. In other words, the size of the receiver defines the size of the region that may be investigated for electrical characteristics. Working in cooperation with these two elements are a conventional source of electromagnetic energy which feeds the same to the antenna for transmission, and a conventional demodulator circuit connected both to this source and to the receiver for monitoring the amplitude of a signal received by the receiver and for comparing this signal, in a phase sense, with that produced by the source.
In operation, the antenna is aimed so as to place the other one of its focal points, i.e. that which is spaced from the one near the receiver, closely adjacent the particular region within a body wherein electrical characteristics, such as impedance, are to be monitored. With the source operating, the voltage and current conditions which exist in this space within a body are determined by the instantaneous impedance of such space. These voltage and current conditions are instantaneously reflected, in an inverse fashion, by related voltage and current conditions at the receiver. In other words, respecting whatever occurs impedance-wise at the zone within the body which is being investigated, related electrical changes occur at the location of the receiver.
Through monitoring, or perhaps more accurately through demodulating, the received signal, to detect amplitude and to compare phase with that of the source, what occurs electrically at the receiver is directly interpretable as an indication of impedance, and/or instantaneous changes of impedance, in the investigated zone. Through such monitoring, and through an understanding of what physical conditions within the zone produce such impedance conditions, the desired physiologic or other conditions within the investigated zone are determinable.
The operation just described may be performed at a relatively low power level. Hence, the likelihood of radiation damage in the investigated zone is extremely low. Further, it is an extremely simple matter to locate the investigated zone wherever desired. This may be done simply by shifting the location and/or orientation of the antenna relative to the investigated body. Further, the resolution of the system is easily controlled through selection of the size of the receiver. More specifically, a larger zone, with lower resolution, may be achieved through using a larger receiver located a somewhat greater distance from its adjacent focal point of the antenna. Greater resolution, with investigation of a smaller zone, is achieved by going in the reverse direction, i.e. through using a smaller receiver located closer to its adjacent focal point. Obviously, the investigation performable by the apparatus of the invention does not require any physical invasion of the body wherein investigation is made.
These and other objects and advantages attained by the invention will become more fully apparent as the description which now follows is read in conjunction with the accompanying drawings.